Superregenerative receiver circuits



W. R. KOCH SUPER-REGENERATIVE RECEIVER CIRCUIT Nov. 12, 1946.-

aai/vc# Frewa/cr Filed June 25 frit/Hvar lill- (Zitomeg Patented Nov. 12, 1946 SUPERREGENERATIV E RECEIVER CIRCUITS Winfield R. Koch, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 25, 1942, Serial No. 448,340

(Cl. Z50-20) 16 Claims.

My present invention relates to super-regenerative receiver systems, and more particularly to receivers of the latter type utilizing self-quenching action.

Super-regenerative receivers of the selfquenching oscillator type are Well known, Usually in such types of receivers the super-regenerative detector includes in its signal input circuit a resistor-condenser network which functions to provide the interruption, or quenching, action at a super-audible frequency. In such a super-regenerative detector of the self-quenching type the quenching action causes a change in average plate current depending upon the amplitude of the signal carrier. Amplitude modulation of the carrier causes the average plate current value to follow at the modulation frequency. On the other hand where frequency modulated carrier energy (FM) is received, the input circuit of the detector is somewhat mistuned from the center frequency of the applied FM signals thereby transforming the FM signal energy to corresponding amplitude modulated carrier energy (AM). Thereafter, the transformed amplitude modulated carrier energy causes the average value of the plate current of the super-regenerative detector tube to follow at the modulation frequency.

Usually there is a utilized a counter type of resistor-condenser network in the plate circuit of the super-regenerative detector. The modulation signal voltage is developed by the integrating action of the resistor-condenser network. However, the sensitivity of such a detection circuit is relatively small, and, hence, there is relatively inefdcient production of modulation signal voltage. Furthermore, considerable noise is produced between station channels.

I have discovered that the quenching frequency in a Super-regenerative detector of the selfquenching type is dependent to al substantial extent upon the applied signal amplitude. I have found that variations in the received signal am- Dlitude can be made to cause substantial variations in quench frequency, and that such variations in quench frequency can be subjected to discriminator action thereby greatly to improve the modulation signal voltage output and greatly to reduce the noise sensitivity when tuning between station channels.

It can be stated, then, that itis one of the main objects of my present invention to provide a super-regenerative detector circuit of the selfquenching type7 and upon whose tuned input circuit may be applied either amplitude modulated carrier energy or frequency modulated carrier energy; variations in quench frequency being translated into variable uni-directional currents which correspond to, and follow, the modulation which originally existed lon the received carrier.

Another important .object of this invention is to provide a novel method of improving the modulation signal voltage output of a super-regenerative detector by taking advantage of the fact that the quench frequency is a function of Vapplied signal amplitude variation, and quench frequency variations being subjected to a discriminator network thereby greatly to increase the variations in modulation signal output current for given received signals.

Another object of the invention is to provide a super-regenerative receiverl employing ,a selfquenching oscillator whose signal input circuit is of the loop type; there being employed a quench frequency detector having a discriminator input circuit to derive modulation signal frequency from variations in quench frequency caused by signal amplitude variation.

Still another object of the invention may be stated to reside in the provision of a novel method of receiving radio signals whether of the FM type or AM type, which method 'comprises generating oscillations at the frequency of the received carrier, `quenching the generated oscillations at a predetermined super-audible frequency thereby to provide high selectivity and gain, deriving from the quenching of the oscillations at carrier frequency additional currents in the quench frequency range whose frequency varies in accordance with amplitude variations of the signal car rier, and translating frequency variations of the quench frequency currents into amplitude variations of the last named currents, and rectifying the amplitude variations to produce modulation signal currents therefrom.

Still other objects of the invention are to improve generally the simplicity and efficiency of super-regenerative receivers, and more particularly to provide super-regenerative receivers of the self-quenching type which are not only reliable in operation, but are economically manufactured and assembled- The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawing:

Fig. l shows a super-regenerative receiver embodying the invention,

Fig. 2 shows the response characteristic of the loop input circuit of the receiver,

Fig. 3 shows the response curve detector input circuit,

Fig. 4 shows a modified form of the invention,

Fig. 5 shows the response curve of the quench detector input circuit of the receiver shownin Fig. 4.

One of the important advantages of the present invention is that the super-regenerative receiver circuits employed may be arranged within a compact casing which is so small that it may readily be fitted into the vest pocket of the user. For this purpose miniature type of tubes are employed, and the energizing direct current sources are of the miniature long-life battery type The reproducer may be of the crystal type, and is preferably of the type used in deaf-aid equipment. Referring to Fig. 1, the transmitted modulated carrier energy is picked up by a tunable loop circuit which comprises a loop I shunted by tuning condenser 2. It is preferred that the loop I be wound within the casing of the receiver. The tuning condenser 2 is to be understood as constructed and designed so as to tune the loop cirof the quench cuit over a relatively wide carrier range. The low potential side of condenser 2 may be grounded.

It is to be understood that the receiver may be used for receiving FM signal energy, or it may be used to receive AM signals. Preferably, reception in the FM band of 42 to 50 megacycles (mc.) is preferred. It is to be clearly understood that by choosing the constants properly the loop circuit may be designed to be tuned over any desired range of station channels. The tube 3 shown is one of the pentode type, and has its cathode 4 connected to an intermediate point on loop I. 'I he control grid 5 is connected to the high potential side of the loop I by a capacitor B, the resistor 'I connecting the grid side of capacitor `Ii to ground. The plate 8 of tube 3 isconnected to a point of proper positive potential by the primary windings of transformer I0. The screen grid II is connected to the lower end of winding 9. Screengrid II and plate 8 have applied to them the positive potential from the direct current source which is not shown. The suppressor grid is established at ground potential. The screen grid I I is bypassed to ground by capacitor I I.

AThe secondary winding I2 of transformer I0 has shunted across it a capacitor I3. Circuit I2I3 is resonated to substantially the quench frequency FQ. Diode I4 has its anode I5 connected to the high potential side of winding I2, while the cathode IB is returned to ground through resistor I 1. The latter is shunted by capacitor I8. The modulation signal voltage, which may be in the audio frequency range, is taken off from the cathode end of resistor I'I. The modulation signal voltage may be amplified in one or more stages of modulation signal amplification, and the amplified signals will` then be reproduced. Considering, rst, the action of the self-quench ing oscillator which comprises tube 3 and its associated circuits,'it is pointed out that network 6-1 has its time constant so chosen that the oscillations producedb'y virtue of the connection of cathode '4 to an intermediate point on loop I will be quenched, or interrupted, at a predetermined super-audible rate. For example, let it be assumed that network 6-1 is chosen so that the quench frequency FQ is 40 kilocycles (kd). This means that the regenerative feedback to loop circuit I is permitted to occur to an extent such that the circuit is beyond the point of oscillation when regenerative feedback is interrupted. The oscillations are, of course, of carrier frequency. The interruption proceeds at a superaudible rate, with the result that maximum gain and selectivity is secured in circuit 2-I. Network 6 1 might consist of an 82 mmf. (micromicrofarads) capacitor and a 330,000 ohm re sistor.

In Fig. 2 I have shown in a purely qualitative manner the response curve of loop circuit I-2. It will be clearly understood that this curve does not depict the actual characteristic, but merely is illustrative. For AM signal reception the variable capacitor 2 is adjusted so that at ea'ch station reception channel, circuit I-2 will be accurately tuned to the desired signal-modulated carrier frequency. This, of course, will be the midband frequency of the station. Hence, in Fig. 2 there is shown the fact that the tuning adjustment of the loop is at the peak of the response curve for AM signal reception. In such case, I have found that there flows in the plate circuit of tube 3 a current whose magnitude is a function of the quench frequency. I have, also, found that the quench frequency is proportional in magnitude to the carrier amplitude. Hence, the stronger the signal received the higher becomes the quench frequency. The variable plate currents of tube 3 actually vary in frequency in accordance with the signal amplitude at grid 5. Since the signal amplitude at grid 5 is a function of the modulation applied to the carrier at the transmitter, it follows that the frequency variations of the quench frequency current flowing in the plate circuit of tube 3 is a function of the modulation existing on the carrier at grid 5. The carrier currents existing in the plate circuit of tube 3 are not used. For FM reception these currents are mostly at the natural frequency of circuit I-2. In any case the carrier currents are bypassed to ground. Capacitor II bypasses carrier currents in winding 9.

In accordance with one of the objects of my in vention, the frequency variations of the quench frequency currents flowing in the plate circuit of tube 3 are augmented by a, discriminator action following. the plate circuit of tube 3. To secure this augmented action, circuit I2-I3 is preferably adjusted to a frequency such that in the absence of received. carrier energy the circuit I2-I3 is tuned to any frequency along the round top of the response curve shown in Fig. 3. The curve of Fig. 3 is the response curve of the quench detector input circuit I2-I3. Here, again, it is not intended that the curve represent the actual characteristic. It is merely illustrative in nature. In Fig. 3 it is shown that in the absence of received carrier energy circuit I2-I 3 is tuned substantially to FQ. This means that the quench frequency currents, in the absence of received carrier energy, have a frequency substantially coinciding with the frequency of circuit I2-I3, and this frequency is at the peak of the response curve of circuit I 2-I 3.

curve as being the center point about which the quench frequencycurrents vary in frequency under the influence of the signal ampliture variations.- It will be recognized that this is a frequency discriminating action wherein highly magr nied amplitude variation currents are derived from frequency deviations of the same currents .about a center frequency point. In this way, the

variations in frequency in the plate circuit of tube 3 are transformed into magnified corresponding amplitude variations. These amplitude variations are then rectified by diode lll. The rectified voltage Variations across resistor I7 are a faithful reproduction of the modulation originally existing on the carrier at grid 5. It will now be seen that tube 3 and its circuits function as a device for converting the amplitude variations of the received signal to frequency variation of quench currents appearing in the plate circuit of tube 3.

It is, of course, possible to use any discriminator device in place of circuit |2-l3. vThose skilled in the art are fully acquainted with the various types of frequencyy discriminators that may be employed instead of the simple tuned circuit |2-|3. Any circuit which has a sloping output voltage vs. frequency input characteristic may `be utilized to transform the quench current frequency variations into corresponding amplitude Variations. It is also possible to amplify the quench frequency current prior to discrimination.

In Fig. 4 there is shown a modification wherein rthe self-quenching circuit employs a tube 20 of the triode type whose cathode is grounded. The loop '2l is shunted by the tuning capacitor 22. The quenching network comprises capacitor 23 and grid resistor 24. The plate 25 provides the regenerative feedback, as at M, by virtue of a loop section 26 in the plate circuit. The positive potential is applied to plate 25 through a plate resistor 21, whose lowerend is bypassed to ground. A quench amplifier 30 has its input .grid 3| coupled by capacitor 32 to the upper end of plate resistor 21, the grid end of capacitor 32 being returned to ground through a resistor. The quench amplifier tube 30 prevents the discriminator circuit from stabilizing the quench frequency. There is a tendency on the part of the discriminator circuit to stabilize the quench frequency currents and thereby prevent the desired frequency variations in the quench currents. work between tubes 20 and 30 is designed to transfer the 40 kc. quench currents.

The discriminator in this case comprises a transformer 4! whose primary and secondary windings are each shunted by respective tuning condensers. Each of the primary and secondary circuits are tuned, in the absence of received carrier energy, substantially .to the quench frequency. The transformer i0 is so constructed, and has its primary and secondary circuits so co-upled,l that it has a substantially fiat-topped response curve as shown in the response curve illustrated in Fig. 5. The sides of the response curve are relatively steep. Hence, when modulated carrier energy is received operation will be had along the steep slope of the curve thereby to give increased amplitude variations for the same frequency deviations of the quench current.

The rectier 50 is used to rectify the amplitude-variable quench current. In this case the anode of diode 50 is connected to the high potential side of the secondary circuit of transformer 40.

The load resistor 5l is connected between the low potential side and ground, and the modulation signal voltage is taken olf from the upper end of The coupling netload resistor 5|. It will be understood'that in place of a single rectifier 50, or single rectier I4 in Fig. l, there may fbe utilized the balanced rectiers known in FM detection circuits. For eX- ample, there may be employed discriminator-rectiiier networks of the type shown by S. W, Seeley in U. S. Patent 2,121,103 granted June 21, 1938; or a discriminator-rectifler of'the type shown by J. D. Reid in U. S. Patent 2,279,506, granted April 14, 1942. There could also be used an FM detector of the type using oppositely mistuned circuits with a balanced detector of the type shown by G. Mountjoy, U. S. Patent 2,280,530, granted April 2l, 1942.

For FM signal reception the variable capacitor 2 of Fig. l will be adjusted as shown in Fig. 2, so that the center frequency of the FM signal energy will fall on one side or the other of the peak of the response curve of the loop circuit. As is well known, such mistuning results in transformation of the received FM energy into corresponding AM signal energy. The transformed AM signal energy is then treated in the same manner as has been described previously for AM signal reception. In this case the tube 3 (or tube 2D) acts as a super-regenerative trans-modulator.

To recapitulate the important features of this invention, I have provided a discriminator circuit following the self-quenching oscillator, which discriminator circuit transforms small changes in quench frequency into large changes of quench current amplitude thereby giving a large modulation signal voltage output from the following rectifier. Furthermore, by using a tuned circuit as a discriminator large voltages can be developed and applied to the subsequent rectier. The circuit therefore exhibits greater sensitivity than the usual super-regenerative circuit. Either side of the response curve shown in Fig. 3, or Fig. 5, can be used. In addition, however, by setting the quench discriminator circuit frequency to a slightly lower frequency than the quench frequency when receiving a signal, the well known background noise of a super-regenerative receiver, in the absence of signals, can be greatly reduced.

The quench frequency in the absence of signals will be somewhat lower, and practically at the top cf the response curve of the quench current discriminator circuit. Variations of quench frequency in such case then produce practically no change in amplitude, because of the round top portion of the selectivity curve. However, When signals are received they cause an increase in the average quench frequency so that the resulting quench voltage has considerable amplitude variation by virtue of operation along the high frequency side of the response curve. The quench current discriminator circuit tuning for maximum audio output is not generally the same as for minimum noise-signal noise. Hence, the discriminator circuit should be -set for whichever improvement is desired. Of course, either of tubes 3 or 20 may be preceded by an amplifier to prevent radiation. The circuits shown may be employed as the I. F. amplier and detector of a superheterodyne receiver, for the same reason.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is:

1. A method of receiving modulated carrier wave energy which comprises regenerating the energy to a high degree, interrupting the regeneration at a predetermined frequency thereby to provide interruption current Whose frequency is a function of the amplitude modulation of said carrier energy, transforming the interruption current frequency variations by frequency discrimination into corresponding amplitude variations, and deriving signal voltages from the resulting amplitude variable interruption current corresponding to the modulation on the received carrier.

2. In a system for receiving modulated carrier Wave energy, a regenerative amplifier tube provided with a carrier wave energy input circuit tuned substantially to a desired carrier frequency, means in the input circuit of said tube for providing self-quenching oscillations at a superaudible frequency, means coupled to the output circuit of said tube for translating frequency deviations of quench current into corresponding amplitude variations, and means for rectifying the amplitude variable quench current so produced.

3. In a super-regenerative receiving system, means for regenerating received modulated carrier Wave energy, means for interrupting the regeneration at a super-audible frequency, means producing interruption currents of variable frequency which correspond to the modulation on the received carrier energy, and frequency discrimination means for producing corresponding amplitude variations of the interruption currents.

4. In a method of receiving frequency modulated carrier Wave energy in a super-regenerative receiving system, translating the received energy into corresponding amplitude modulated carrier wave energy, regenerating the translated energy, quenching the regeneration at a super-audible frequency, deriving quench current variable in frequency in accordance with original modulation of the received carrier energy, translating the frequency variations of the quench current into corresponding amplitude variations, and detecting said translated amplitude variations.

5. In a super-regenerative receiving system, a self-quenching oscillator circuit having a tuned input circuit resonated to substantially a desired carrier frequency, means in circuit with the input circuit for producing quenching action at a super-audible frequency thereby to provide quench currents whose frequency is a function of the modulation on the received carrier, means for amplifying the quench current, and frequency responsive means, responsive to said variable frequency quench currents, for providing voltage corresponding to the modulation originally applied to the received carrier.

6. A method of receiving radio signals in a self-interrupted oscillator system, which includes applying said signals to said system, separating out current of the interruption frequency, and detecting said separated current subsequent to separation.

7. A method of receiving radio signals which includes self-quenching super-regenerative detection of said signals, selection of quench-frequency currents, and frequency discrimination and subsequent rectification of said currents.

8. A method of receiving radio signals in an oscillating system including application of said signals to a circuit oscillating at approximately the same frequency as the signals, interruption of the oscillation-s at a super-modulation rate,

selection of currents of said interruption frequency, subjection of the selected currents to frequency discrimination, and rectification of the resulting currents.

9. A method of receiving angular velocitymodulated carrier wave energy which comprises regenerating the energy to a high degree, interrupting the regeneration at a predetermined frequency, transforming by frequency discrimination resulting interruption current frequency variations into corresponding amplitude variations, and deriving from the resulting interruption current of varia-ble amplitude voltages corresponding to the modulation on the received carrier.

10. In a system for receiving frequency modulated 4carrier Wave energy, a tube provided with a carrier wave energy input circuit tuned substantially to a desired carrier frequency, said input circuit acting like a sloping filter, means in the input circuit of said tube for providing self-quenching oscillations at a super-audible frequency, means for regenerating the input circuit, means coupled to the output circuit of said tube for translating frequency deviations of quench current into corresponding amplitude variations, and means for rectifying quench current so produced.

11. In a super-regenerative receiving system, means for regenerating received modulated carrier Wave energy to the point of oscillation, means for interrupting the regeneration at a superaudible frequency, means producing interruption currents of variable frequency which correspond to the modulation on the received carrier energy, and a sloping lter means for producing corresponding amplitude variations of the interruption currents.

12. In a method of receiving modulated carrier Wave energy in a super-regenerative receiving system, regenerating the energy to the point of oscillation, quenching the regeneration at a super-audible frequency, deriving quench current variable in frequency in accordance with original modulation of the received carrier energy, translating the frequency variations of the quench currents into corresponding amplitude variations, and detecting said amplitude variations.

13. In a super-regenerative receiving system, a self-quenching oscillator circuit having a tuned vinput circuit resonated to substantially a desired carrier frequency, means in circuit with the input circuit for producing quenching action at a superaudible frequency thereby to provide quench currents Whose frequency is a function of the modulation on the received carrier, means for amplifying the quench current, and a tuned circuit discriminator means, responsive to said variable frequency quench currents, for providing voltage corresponding to the modulation originally applied to the received carrier.

14. In combination with a self-quenching oscillator of the super-regenerative type provided with a tunable loop input circuit, a quench current detector provided with a resonant input circuit tuned to the quench frequency in the absence of received modulated carrier energy, and means transferring frequency-variable quench currents from the oscillator to said input circuit.

l5. In combination with a self-quenching oscillator of the super-regenerative type provided with a tunable loop input circuit, a quench current ,detector provided with a resonant input circuit tuned to the quench frequency in the absence of 75 received modulated carrier energy, and means in the input circuit to provide self-quenching action; the improvement which comprises a rectier provided with a frequency discriminator input circuit, and means for transmitting to the discrimnator input circuit quench currents of variable frequency developed in the detector tube output.

WINFIEID R. KOCH.

Disclaimer 2,410,981. Wn7eld R. Koo/L, Haddoneli'N. J. VlSUPERREGMIEPATIVE RE- CEIVER CIRCUITS. Patent dated Nov. 12, 1946. Disclaimer led Mar. 13, 19,51, by the assignee, Badia Corporation 0f Amevz'ca.

`Hereoy enters this disclaimer t0 claims 1 2, 3, 6, 7, and 8 of said patent.

[Oyjcz'al Gazette April 24, 1951.] 

